The semiconductor integrated circuit (IC) industry has experienced rapid growth. In the course of IC evolution, functional density (i.e., the number of interconnected devices per chip area) has generally increased while geometry size (i.e., the smallest component (or line) that can be created using a fabrication process) has decreased. This scaling down process generally provides benefits by increasing production efficiency and lowering associated costs. However, such scaling down has also been accompanied by increased complexity in design and manufacturing of devices incorporating these ICs, and, for these advances to be realized, similar developments in device fabrication are needed.
As merely one example, advances in lithography have been important to reducing device size. In general, lithography is the formation of a pattern on a target. In one type of lithography, referred to as photolithography, radiation such as ultraviolet light passes through or reflects off a mask before striking a photoresist coating on the target. The photoresist includes one or more components that undergo a chemical transition when exposed to radiation. A resultant change in property allows either the exposed or the unexposed portions of the photoresist to be selectively removed. In this way, photolithography transfers a pattern from the mask onto the photoresist, which is then selectively removed to reveal the pattern. The target then undergoes processing steps that take advantage of the shape of the remaining photoresist to create features on the target. Another type of lithography, referred to as direct-write lithography, uses a laser, an electron beam (e-beam), ion beam, or other narrow-focused emission to expose a resist coating or to pattern a material layer directly. E-beam lithography is one of the most common types of direct-write lithography, and, by directing a collimated stream of electrons to the area to be exposed, can be used to remove, add, or otherwise change a resist or other material with remarkable accuracy.
Because of the manner in which the resist pattern defines the features to be formed, feature quality depends heavily on the ability of the resist to form edges at boundaries between exposed and unexposed areas that are both precise and stable. In contrast, irregular resist edges may lead to narrowing, necking, bridging and other feature defects. In this way and others, resist performance directly affects critical dimension (CD) and other measurements of feature size and quality. While existing resists have been generally adequate, additional improvements hold the potential to produce smaller circuits and to improve fabrication yield.